This article is an empirical contribution to the field of educational technology but also - and above all - a methodological contribution to the analysis of the activities enacted in this field. It takes account of a pilot study conducted within the framework of doctoral research and consisted in describing, analysing and modelling the activity of a trainee teacher in a situation of autonomous use of a video-based digital learning environment (DLE). We were particularly careful to describe the method in great detail. Two types of data were collected and processed within the framework of "course-of-action": (i)activity observation data (dynamic screen capture) and (ii) data from resituating interviews supported by digital traces of that activity. The findings (i) validate the method's relevance in relation to the object and issues of the research, (ii)show different levels of organization in the activity deployed in the situation of use, (iii) highlight four registers of concerns orienting use of the DLE. We conclude from a perspective of educational technology, by discussing how, according to certain conditions and different time scales, the findings inform a process of continuous DLE design.